The chemical, 2,4-dinitrophenylhydrazine, had the potential to be explosive and could have blown out windows and doors in the lab.

It was discovered during a routine audit of chemicals at Ashbourne Community School in Co Meath yesterday morning.

The school was closed for the summer holidays and no students were in the building.

The Army removed the chemical to nearby waste ground where they carried out a controlled explosion.

The chemical is used in science labs in schools and colleges during experiments. It is used to help test for aldehydes and ketones, simple compounds which contain a carbon-oxygen double bond. It normally has a honey-like consistency and is relatively safe. However, it can harden and crystallise and it then becomes dangerous.